Optical borate glass



- 1963 c. WEISSENBERG ETAL 3,081,178

OPTICAL BORATE GLASS Filed Aug. 10, 1959 2 Sheets-Sheet l Fig'./

INVENTORS m mm,

March 12, 1963 a. WEISSENBERG ETAL 3,031,178

OPTICAL BORATE GLASS Filed Aug. 10, 1959 z Sheets-Sheet 2 IN YENTORS United States Patent 3,081,178 OPTICAL BORATE GLASS Gustav Weissenberg and Otto Ungernach, Marburg (Lahn), Germany, assignors to Ernst Leitz, G.m.h.H., Wetzlar (Lahn), Germany, a corporation of Germany Filed Aug. 10, 1959, Ser. No. 832,594 6 Claims. (Cl. 10647) The present. application is a continuation-in-part of our co-pending application Ser. No. 271,804, filed February 15, 1952, and now abandoned.

The above invention relates to practically fluorine free optical borate glasses which are free from toxic and radioactive crude materials. The glasses exhibit a high index of refraction with a relatively low dispersion.

Glasses of similar optical bases are known in the art. However besides oxides of the rare earths, particularly lanthanum oxide they contain almost always thorium oxide, which is of only limited usefulness because of its radioactivity. Other known glasses. contain beryllium oxide which is exceptionally toxic. Their preparation and working requires very expensive special protective meas ures whose action is still very problematical.

The glasses of our invention are characterized in that:

3,081,178 Patented Mar. 12, 1953 with the fluorides present to form boron trifluoride. The melting process is then also so conducted regarding the melting temperature and the time of melting that the fluorine originally present" will be practically quantitatively driven out of the melt as boron trifluoride. In this care is to be taken that, always according to the alkaline. earth metal compound used, the time varies for practically it is suitable for reducing the melting down temperature to add cryolite as a flux in an amount up to 2% by weight of themelting charge.

In FIGS. 1 to 4 of the accompanying drawings are shown, in the three coordinate diagrams, the boric oxide- First, they consist of at least 80% ot a glass base of boric oxide, lanthanum oxide and at least one oxide of the alkalineearth metals, magnesium, calcium, strontium and barium in which the mol ratio of theoxide of the alkaline earth metals to boric oxide lies between 0.2 and 1, and the mol ratio of lanthanum oxide to boric oxide lies between 0.1 and 0.5.

Secondly, they contain from to 20% by weight of at least one oxide of the elements of the group consisting of germanium, tin, zirconium and tantalum, as also T-hirdly, they contain from 0 to 5% by weight of silica] and aluminum oxide. The lanthanum oxide can, in accordance with the invention, be substituted in part by at least one oxide or the elements of the group consisting of indium and yttrium.

The amount of germanium oxide can amount up to by weight, the amount of zirconium oxide up to by weight, the amount of tin oxide up to 5% by weight and the amount of tantalum oxide up to 20% by weight.

The alkaline earth elements can be introduced into the mixture to be melted down as oxides or in the form of such compounds as change in the melt to oxides as, for example, carbonate, nitrate and the like. In this it is noted that the melting temperature and duration of melting will be so selected that by way of example in the use of carbonates the carbon dioxide is driven out quantitatively. The alkaline earth metals can also be introduced into the-melt charge as fluorides if, at the same time an increased amount of boric oxide is introduced which exceeds the limits given above for the mol ratio. The required addition of boric oxide is determined by calculating the additional amount of boric oxide required to combine lanthanum oxide-alkaline earth oxide in percent. by weight of the glass base in the range in which they are found in the glass formation of our invention. In these drawings:

FIG. 1 shows the glass is which the alkaline earth oxide is magnesium oxide;

FIG; 2 shows the glass in which the alkaline earth oxide is calcium oxide;

FIG. 3 shows the glass in which the alkaline earth is strontium oxide, and

FIG. 4 shows the glass in which the alkaline earth oxide is barium oxide.

These ranges are recalculated from the above stated mol ratios to percent by weight. Within these ranges a large number of valuable glasses will be melted. The completion of a small number of these glasses is shown in the following tables. a

g In Table 1 are given examples which consist in partonly of the glass base and in part of the glass base and the addi tives given above. The data of the table are in percent by weight. In two particular cases the mol ratio of alkaline earth oxide: boric oxide and lanthanum oxide: boric oxide respectively are additionally given.

' Table2 shows some examples in which the lanthanum oxide is substituted in part by indium oxide and yttrium oxide.

Table 1 M01 ratio Percent by weight Glass Melt No. MeO La Og m 0., base,

percent B203 113. 03 C30 ZIO: T3205 B103 .A2/0l/W 40. 53. 6 6. 4 0.200 0. 288 1. 723 54. 3 100 A 37. 33. 3 12. 5 4. 2 12. 5 O. 415 0. 190 1. 731 49. 9 83 Mol ratio Percent by weight Glass Melt No. MeO LflzOa no 0., base,

percent B203 Lagos S10 I S102 S1101 T8305 B203 1 34/0 35. l 36. 4 28. 5 0. 548 0. 224 1. 709 53. 3 100 Z B2/X 22. 5 52. 5 6.7 4 l 4. 1 10. 1 0.200 0. 500 1. 789 47. 3 81. 7 g

M01 ratio Percent by weight Glass Melt No. MeO 113203 m u.. base,

percent B103 113703 B30 S102 G801 T3505 B203 G2/a 23. l 50. 5 10. 1 2. 5 6. 9 6. 9 0.200 0. 470 1. 774 48. 6 83. 7

Mol ratio Percent by weight Glass Melt No. MeO Lao. m "a base,

percent B 03 Lagos MgO I S: I Geo: ZlOg B203 MglG 45.9 31. 6 I 5. 8 I I 16. 7 0.221 0.148 1. 717 49. 7 83. 3

Table 2 M01 ratio Percent by weight Glass Melt No. MeO Lazoa m Ue base,

percent B203 La Os YzOa I CEO I S10: Z109 B703 YV2 32. 3 40. 3 12.2 I 5. 2 I 5.0 5.0 0. 201 0. 385 1. 715 53. 3 90 M01 ratio Percent by weight Glass Melt No. MeO L020 ne 0., base,

percent B103 Lagos 11110 CaO I SiOz I ZrOg B203 InV3 32. 3 40. 3 12. 2 5. 2 I 5.0 I 5. 0 0.201 0. 364 1. 705 51. 3 90 Having described our invention, what we claim is: 1. Optical glass having an index of refraction (11,.) above 1.7 and an Abb number above 47 and consisting essentially of (1) at least 80% by weight of a mixture of boric oxide, lanthanum oxide and at least one oxide of the group of alkaline earth metals consisting of magnesium, calcium, strontium and :barium, in which the mol ratio of the alkaline earth metal oxide to the 65 boric oxide is between 0.2 and 1 and the mol ratio of the lanthanum oxide to the boric oxide is between 0.148 and 0.5;

(2) of 0 to by weight of at least one oxide of the oxide is substituted at least in part by at least one oxide of elements of the group consisting of yttrium and indium. 3. Optical glass of claim 1 germanium oxide in amount to from 0 to 10% by weight.

4. Optical glass of claim 1 zirconium oxide in amount to from 0 to 20% by weight.

5. Optical glass of claim 1 tin oxide in amount to from 0 to 5% by weight.

6. Optical glass of claim 1 tantalum oxide in amount to from 0 to 20% by weight.

References Cited in the file of this patent UNITED STATES PATENTS Re. 21,175 Morey Aug. 15, 1939 ziffii g i sg z germamum zlmmum 2,466,510 Sun et a1. Apr. 5, 1949 (3) of 0 to 5% by weight of the group consisting of FOREIGN PATENTS silica and aluminum oxide. 462,304 Great Britain Mar. 3, 1937 2. Optical glass of claim 1 in which the lanthanum 608,298 Great Britain Sept. 13, 1948 

1. OPTICAL GLASS HAVING AN INDEX OF REFRACTION (NE) ABOVE 1.7 AND AN ABBE'' NUMBER ABOVE 47 AND CONSISTING ESSENTIALLY OF (1) AT LEAST 80% BY WEIGHT OF A MIXTURE BORIC OXIDE, LANTHANUM OXIDE AND AT LEAST ONE OXIDE OF THE GROUP OF ALKALINE EARTH METALS CONSISTING OF MAGNESIUM, CALCIUM, STRONTIUM AND BARIUM, IN WHICH THE MOL RATIO OF THE ALKALINE EARTH METAL OXIDE TO THE BORIC OXIDE IS BETWEEN 0.2 AND 1 AND THE MOL RATIO OF THE LANTHANIUM OXIDE TO THE BORIC OXIDE IS BETWEEN 0.148 AND 0.5; P(2) OF 0 TO 20% BY WEIGHT OF AT LEAST ONE OXIDE OF THE ELEMENTS CONSISTING OF GEMANIUM, TIN, ZICONIUM AND TANTALUM; (3) OF 0 TO 5% BY WEIGHT OF THE GROUP CONSISTING OF SILICA AND ALUMINIUM OXIDE, 